Determining concrete strength by using small-diameter cores

Synopsis Estimates of concrete strength are often made from compression tests on cores which have a diameter considerably less than the recommended 100 mm. The paper examines the results of a laboratory investigation in which 44 mm diameter cores were cut and tested. The influence of both specimen and aggregate size upon height/diameter ratio and orientation effects is examined, and observed relationships between core strengths and measured control cube strengths are compared with those normally used for larger cores. It is shown that core strength is affected by both specimen size and aggregate size, and it is proposed that conversion to corresponding cube strengths should take this into account. The variability of results is also assessed in relation to the above factors, and an estimate made of the accuracy of predicted actual cube strength that is likely to be achieved from testing cores of this size.